We present a case of adult Pompe disease (acid maltase deficiency) with an uncommon clinical presentation characterized by severe fatigue and myalgia prior to the onset of limb girdle weakness. Remarkably, the muscle biopsy demonstrated selective involvement of type 1 muscle fibers. The cause and clinical effects of fiber type specific involvement are currently unknown, but the phenomenon might contribute to the clinical heterogeneity in Pompe disease and the variable response to enzyme replacement therapy.